Intrusion detection apparatus having antijamming protection system

ABSTRACT

This disclosure includes an intrusion detection system with a motion alarm which responds to a Doppler frequency signal. The motion-related Doppler frequency signals cover a predetermined frequency band and the alarm circuit is constructed to respond to all signals above a selected minimum amplitude within such band. A supervisory alarm is also provided which responds to a frequency higher than any frequency within such band. A jamming alarm circuit is provided which responds to a signal above a selected amplitude greater than the motion alarm selected amplitude and essentially independent of frequency.

United States Patent 13,618,083

[72] Inventors Billy Burley; 3,224,002 12/1965 Carre 343/18 E Frank S. Kett, Dallas; Geoffrey A. Young, 3,242,486 3/1966 Corbel]. 343/5 PD Irving; Paul I. Corbell, Dallas, all of Tex. 3,378,834 4/1968 Corbell. 343/5 PD [21] Appl. No. 805,622 3,383,678 5/1968 Palmer 343/5 PD [22] Filed Mar. 10, 1969 3,465,336 9/1969 Fishbein et al 340/258 A X [45] Patented Nov. 2, 1971 [73] Assignee Johnson Service Company Milwaukee, Wis.

Primary ExaminerMalcolm F. Hubler Attorney-Andrus, Sceales, Starke & Sawall [54] INTRUSION DETECTION APPARATUS HAVING ANTIJAMMING PROTECTION SYSTEM ABSTRACT: ThlS disclosure Includes an intrusion detection [52] US. Cl 343/5 PD, system with a motion alarm which responds to a Doppler 340/258 343/77, 343/18 E frequency signal. The motion-related Doppler frequency [51] Int. Cl G0ls 7/36, signals coveta predetermined frequency band and the alarm G015 9/42 Gosh 13/24 circuit is constructed to respond to all signals above a selected [50] Field of Search 343/5 PD, minimum amplitude within Such band; A supervisory alarm is 18 E; 340/258 A also provided which responds to a frequency higher than any fre uency within such band. A jamming alarm circuit is pr0- [56] Reierences cued vid ld which responds to a signal above a selected amplitude UNITED STATES PATENTS greater than the motion alarm selected amplitude and essen- 3,111,657 11/1963 Bagno 340/258 A tially independent offrequency.

MODULATOR SUPERVISORY ALARM ALARM CIRCUIT INTRUSION DETECTION APPARATUS HAVING ANTLIAMMING PROTECTION SYSTEM This invention relates to an intrusion detection apparatus having means to prevent desensitizing of the apparatus by impressing a jamming signal in the receiving means.

Intrusion detection systems have been developed employing microwave energy within the area to be protected. A receiving means is mounted to receive at least an intruder intercept related portion of the transmitted energy, either directly or as a reflected signal from a body or target moving within the area being protected. The motion of a body or target within the area generates a Doppler frequency signal in the receiving means which results in the triggering of an alarm. For example, highly satisfactory systems are shown in the Corbell U.S. Pat. Nos. 3,242,486 and 3,378,834 employing amplitude discrimination of a single cycle of an amplified Doppler frequency motion signal to trigger an alarm. As disclosed in the two patents, a Klystron tube is employed to establish a microwave signal in the X-band portion of the spectrum and a supervisory control signal is preferably superimposed upon the microwave signal to insure that the detection system is in proper operating condition at all times. In the first Corbell patent, a lowlevel background signal of the Doppler frequency but of insufficient peak amplitude to operate the alarm is employed in connection with a signal integrating circuit to produce a supervisory control signal. The low-level background signal is obtained by employing a poorly filtered energization circuit driving the Klystron tube. For example, the Klystron may be pulsed with 4 kHz. (Hertz) modulation as a result of the improper filtering and superimposed upon a 10.525 GI-iz. transmitted signal.

The second Corbell patent suggests an improvement par ticularly for a perimeter-type system wherein the transmitter Klystron source pulsed by the action of a DC to DC converter supply to superimpose a high-frequency signal on the transmitted signal. For example, a 5,000 Hz. signal may be inserted to pulse the Klystron microwave source and thereby provide a signal of a frequency substantially greater than the motion detection Doppler frequencies. This supervisory frequency signal is substantially removed from the Doppler frequency signals and the two signals are essentially isolated at the receiving means by suitable filtering means.

In using the background or apparent Doppler frequency signal, there is some danger of mistriggering of the circuit by response to the supervisory signals as if there were an actual intrusion. In the pulsed control circuit, the substantially higher frequency of the supervisory signal requires that the common amplifier be shaped to pass both the motion-related Doppler frequency and the high modulation frequency. The gap in the amplifier characteristic between the motion-related Doppler band and the supervisory band has been found to establish a potentially vulnerable jamming area. An intruder with highly sophisticated equipment can detect the operating frequency characteristics of the detection unit and by properly feeding a signal intermediate the Doppler frequency signals and the supervisory frequency signals saturate the detection amplifier without triggering of either the supervisory or alarm circuitry. The system is thereby desensitized and cannot readily detect the Doppler frequency signals established by target motion and consequently cannot properly detect intrusion. Although the jamming would require sophisticated apparatus and the like, the possibility of jamming is considered undesirable for unusually high-security applications, such as for example, are found in many governmental requirements.

The present invention is particularly directed to an antijamming means for detecting the attempted jamming of the detection system.

In accordance with the present invention, the intrusion detection system includes means for establishing a microwave field in the area to be protected with a moving target creating a Doppler frequency signal in a receiving means. An alarm circuit is connected to respond to a motion-related Doppler frequency. The motion-related Doppler frequency signals cover a predetermined frequency band and the alarm circuit is constructed to respond to all signals within such band. The alarm circuit is preferably constructed to respond to motion related Doppler frequencies above a selected minimum amplitude as disclosed in the Corbell U.S. Pat. No. 3,242,486. A supervisory signal of a frequency higher than any frequency within said-band may be continuously transmitted to the receiving means. A jamming alarm circuit is also connected to the output of the receiving means and is constructed to respond to an output signal above a selected amplitude and essentially independent of frequency. The jamming responsive amplitude is selected to be greater than the motion alarm selected amplitude. The jamming alarm circuit will not therefore respond to the motion related signals or to the supervisory signals. However, if an attempt is made to saturate the receiving means, the output of the receiving means increases to and above the jamming alarm level and triggers the jamming alarm circuit.

The antijamming circuitry may advantageously include a shaping filter network to increase the sensitivity with frequencies above the normal motion-relatedDoppler frequencies and to thereby compensate for the decreasing gain of the receiver amplifying means.

In accordance with a novel feature of the invention, an alarm signaling means is conjointly controlled by the motion alarm circuit and by the antijamming alarm circuit while a different supervisory signal means is controlled by the supervisory circuit. This permits distinguishing between a relatively serious fault associated with an intruder or possible intruder and relatively lesser fault associated with a malfunctioning of the system components.

In a particularly satisfactory system, the alarm detecting circuit includes a transistorized switching circuit connected in circuit with the motion alarm circuit to conjointly control a motion alarm device such as a relay. Generally, in this aspect of the invention, both the motion alarm circuit and the antijamming alarm circuit include normally conducting transistors connecting in series with the alarm device and holding the alarm device in a standby position. If a motion-related signal actuates the motion alann circuit, the related transistor is turned off and the alarm device actuated to signal the fault. Similarly, if a jamming signal actuates the related antijamming alarm circuit, the related transistor is turned off and the alarm device similarly actuated to signal a fault.

The present invention thus provides an improved supervisory control of the antidetection system particularly for highsecurity application.

The drawing furnished herewith illustrates the best mode presently contemplated by the inventors for carrying out the subject invention in which the above advantages and features are clearly disclosed, as well as others, which will be readily understood from the following description of such embodiment.

In the drawing:

FIG. 1 is a diagrammatic illustration of an intrusion detection apparatus incorporating the subject matter of the present invention; and

FIG. 2 is a schematic circuit diagram showing a preferred construction including details of an antijamming circuit shown in block diagram in FIG. 1.

Referring to the drawing, and particularly to FIG. 1, the illustrated embodiment of the invention includes preferred transmitting and receiving systems generally in accordance with the teaching of the copending application of Bailey et al. entitled Intrusion Detection Apparatus Having Supervisory Control Means which was filed on Mar. 10, 1969, bearing Ser. No. 805,591 and which is assigned to the same assignee. The several components more fully described in such application are therefore described herein only in such detail as to provide a complete understanding of the present invention. Generally, the illustrated detection system includes a microwave transmitter oscillator l coupled to a transmitting antenna 2 and adapted to establish a microwave energy field or beam 3. A target 4, such as a moving person within the energy field 3, establishes a reflected energy beam or field 5 which is related to the motion of the target. A receiving antenna 6 is mounted in the illustrated embodiment of the invention adjacent the transmitting antenna 2 to intercept the reflected signal or energy field and transmit a related signal to a suitable receiver 7.

A supervisory modulator 8 is connected to modulate the output of the transmitter oscillator l and create a supervisory signal of a preselected frequency. The transmitter oscillator 1 is also directly coupled to the receiver 7 as by the coupling line 9 to continuously transmit a portion of the output of the transmitter oscillator 1 to the receiver 7. The receiver may include a well-known crystal detector and mixer 10 which transmits the Doppler signals to an amplifier 11. The output of the amplifier l 1 is connected in common to a motion alarm circuit 12 to a supervisory alarm circuit 13 and in accordance with the present invention to antijam circuit 14. The supervisory alarm circuit 13 is interconnected to actuate a supervisory alarm such as a supervisory alarm relay 16 connected to a suitable alarm device such as a bell, not shown. The motion alarm circuit l2 and the antijam alarm circuit 14 are connected to conjointly control a motion alarm such as a motion alarm relay 17 such as a different bell, not shown.

The present invention is particularly adapted to the supervised circuitry disclosed in the above copending application wherein the amplifier 11 is constructed to have a gain characteristic including an essentially constant gain over a selected motion related Doppler frequency range or band and to rapidly roll off above such range.

The supervisory modulator 8 establishes a modulation frequency within the rolloff portion of the gain characteristic and preferably just immediately outside the Doppler motion band. In the particular illustrated system, for example, the transmitter 1 established a microwave field of 2.45 61-12. (gigahertz). The motion-related Doppler band covered 1 to I80 Hz. (Hertz) with a modulating frequency signal of 500 Hz. established by the modulator 8 providing a relatively narrow gap between the Doppler frequency motion band and the supervisory frequency.

The supervisory alarm circuit 13 is set to respond to the modulating frequency of 500 Hz. If the transmission of this signal decreases significantly for any reason, the alarm circuit is energized to actuate the supervisory relay 16 and establish an indication of a more or less minor fault.

The motion alarm circuit 12 may advantageously include a Schmitt trigger circuit which responds to a single cycle of a motion-related Doppler frequency signal above a selected amplitude, as disclosed in Corbell US. Pat. No. 3,242,486. If circuit 12 is actuated, the alarm relay 17 is operated to indicate a major fault, that is, an intruder within field 3. The antijam circuit 14 is constructed to establish an output if the amplitude of the output of amplifier 11 increases above the normal level, independent of any frequency limitation. This prevents desensitizing of the system by saturating the amplifier 11 with a modulating signal which does not actuate either of the other two circuits.

A preferred embodiment of the invention is shown in FIG. 2. The transmitter l is a solid state coaxial cavity Clapp oscillator having a coaxial cavity 18 and coupled therethrough to the transmitting antenna 2 in accordance with any well-known or operative connection. The cavity 18 is coupled to the antenna 2 for transmitting of field 3 and through the antenna 2 to antenna 6 to transmit a portion of the energy directly to the receiving means. A voltage regulator 19 connects the oscillator l to a direct current supply shown as a transformer-rectifier network 20 to establish a predetermined direct current bias to the oscillator and thereby establishing the microwave frequency of oscillation and the output frequency of cavity 18.

The regulator 19 includes a solid state integrated circuit 20 to maintain the voltage at the bias line 21 of oscillator l at a closely regulated output voltage and to establish modulation in accordance with the output of the modulator 8.

The supervisory signal modulator 8 is shown as a multivibrator circuit connected to the voltage regulating circuit 20 to modulate the preset regulated DC bias voltage. The circuit 20 thus combines a feedback voltage and the modulating voltage to produce an accurately modulated bias supply.

The output of the Clapp oscillator l is therefore a microwave frequency determined by the DC bias modulated in accordance with the signal from the multivibrator circuit 8. The energy is coupled to the transmitting antenna 2 and to the receiving antenna 6, for example, as shown in the Corbell patent or the copending application of Corbell et al. entitled Waveguide Antenna Structure for intrusion Detection Apparatus, filed on Mar. 10, 1969 bearing Ser. No. 805,590 and assigned to the same assignee.

The receiving means 7 includes the radio frequency detector and mixer 10 which provides an output signal proportional to the transmitted signal and the difierence or Doppler frequency signal. The signal is amplified by the gain amplifier l l and applied to the several alarm circuits.

The Schmitt trigger circuit 22 of the intruder alarm circuit 12 is interconnected to the output of the amplifier 11 through an adjustable potentiometer or resistor 23 which loads the amplifier and controls the output swing of the amplifier and permits adjustment of the effective gain characteristic as seen by the Schmitt trigger circuit. The Schmitt trigger circuit is provided with a filter network not shown, to pass only the Doppler frequencies to thus control the alarm relay 17 in accordance with the amplitude of the Doppler frequency signals within the constant gain characteristic of the amplifier. The trigger circuit may include a variable potentiometer or the like to determine the minimum amplitude of the Doppler frequency signal which is effective to fire or actuate the Schmitt trigger circuit.

In summary, the operation of the illustrated embodiment of the invention is briefly summarized as follows.

The system is set with the transmitter and the receiving antennas 2 and 6 properly located with respect to the control field 3. A particular advantageous packaging is disclosed in the Corbell et al. copending application, identified above. The transmitting oscillator 1 and the audio oscillator 8 are energized to establish the microwave field in cavity 18; modulated in accordance with the output of the audio oscillator 8. The amplifier gain adjustment is set to provide the constant gain over the desired Doppler frequency range with the rolloff adjacent the uppermost frequency to be detected. The modulator is set to provide a modulation signal within the rolloff portion.

If a target moves within the energy field, the movement will create a Doppler frequency signal related to the speed of target movement. The amplitude of the Doppler signal is determined by the range, size and reflective characteristics of the target. The signal is transmitted via the amplifier 11 to the several supervisory and alarm circuits 1244. The Doppler frequency signal is applied to the motion alarm circuit 12 and if it exceeds the amplitude level, it will immediately trigger the corresponding alarm circuit and actuate the related alarm relay 17. If the target range, size or reflective characteristic is such that the Doppler frequencys amplitude is below the set level, no alarm results.

The Doppler frequency signal is applied to the antijam alarm trigger circuit. However, the magnitude is generally insufficient to cause triggering. The Doppler frequency signal is also applied to the supervisory alarm circuit 13, but does effect its function as it is set to respond to the modulation signal.

If the modulating or supervisory signal decreases sufficiently for any reason, the corresponding alarm circuit is actuated to indicate the presence of a fault.

A prospective intruder may introduce an additional modulating signal different from the normal motion related Doppler signals and the supervisory signal for purposes of saturating amplifier 11 and thereby desensitizing the system to the Doppler signals. However, when the output of the amplifier 11 increases above the normal level of the triggering level for the lOl008 0500 motion alarm circuit, the negative half-cycle is transmitted via the network 30 and diode 34 to the base 36 of transistor 29. The negative signal is then sufficiently large to overcome the normal turn-on bias and the transistor 29 turns off, thereby opening the circuit to relay 17. The deenergizing of relay l7 actuates its contacts 27-1 to operate the signaling means for indicating a major fault.

In the illustrated embodiment, the antijamming system actuates the alarm means as the motion of an intruder while the supervisory circuit 13 actuates a different alarm means. Normally, the presence of an intruder and/or an attempt to jam the detection system is of a more serious nature than the failure of the supervisory system. However, the antijamming means may be tied to the supervisory alarm means or to a completely separate alarm means which is the same as or different from either or both of the other alarm means.

The network 30 is constructed to establish a high pass filter. The filter will impede the motion-related frequency signals which however are operative in the intruder alarm circuit 12. At frequencies above the normal motion related frequencies, the filter network 30 increases the sensitivity of the antijamming circuit and compensates for the decreasing gain characteristic of the amplifier. The combination of circuits establishes a reasonably constant antijam detection level which is essentially independent of frequency while protecting the amplifier.

In the illustrated embodiment of the invention, the output of the Schmitt trigger circuit 22 is connected to the input of a solid state control means shown as an NPN-transistor 24 for controlling of the alarm relay 17. The transistor 24 has its base 25 coupled to the trigger circuit 22 and its collector-emitter connected in series between a power supply input 26 and one side of a winding 27 of the relay 17. A biasing network 28 biases transistor 25 to conduct in the absence of the actuation of the Schmitt trigger circuit 22 and thus applies power to one side ofthe relay winding 27.

The opposite side of the winding 27 is connected in a completed circuit by a normally conducting transistor 29 forming the solid state control means of the antijamming circuit 14.

The illustrated antijamming circuit 14 includes a shaping input filter network 30 connected to the amplifier 11. The network 30 includes a pair of series connected capacitors 31 and 32 and a resistor 33 paralleled with the capacitor 32.

A blocking diode 34 is connected to the network 30 and polarized to transmit only the negative half-cycle of the signal from amplifier 11. The positive half-cycle is shunted to ground by a properly polarized diode 35 connected between the network and ground.

The base 36 of the transistor 29 is connected to the blocking diode 34 and to a biasing resistor 37 which is connected to the power supply. The collector-emitter of the transistor 29 is connected in series with the relay winding 27 and a stabilizing emitter-resistor 38 to ground to establish the complete circuit path for energizing of the relay winding 17.

In the above circuit, when both of the transistors 24 and 29 are in the normally conducting state, the relay winding 27 is energized and the motion alarm device is held in standby condition. If either transistor 24 or 29 is turned off or its conductivity is sufficiently reduced, the relay 17 drops out and creates a related alarm to indicate a major fault.

The present invention thus provides a Doppler frequency type intrusion detection system essentially preventing any manner of removing the response to a motion generated signal without establishing an alarm indicating such removal.

We claim:

1. An intrusion detection system, comprising a microwave transmitter means for radiating a microwave field, a receiving and amplifying means located within said field for receiving said field, motion detection means connected to the receiving amplifying means to detect motion related signals above a first selected amplitude, and an antijam detection means connected to said receiving and amplifying means and responsive to an output signal above a second selected amplitude treater than said first selected amplitude and related to a selected signal driving said receiving and amplifying means into saturation.

2. The intrusion detection system of claim ll, having an alarm means, and wherein said motion detection means and said antijam detection means are connected to conjointly hold said alarm means in a standby condition.

3. The intrusion detection apparatus of claim 1 wherein said antijam detection means includes an output means and a high pass filter means connected to the output of the receiving and amplifying means and to the output means whereby the antijam detection means response increases as said motion detection means response decreases.

4. In an intrusion detection apparatus having a microwave transmitting means and a receiving and amplifying means, motion detection alarm means responsive to a motion-related signal within a predetermined range of Doppler frequencies and of selected normal maximum amplitude, and an antijam detection means connected to said receiving and amplifying means and constructed to respond to a selected minimum amplitude output of the receiving and amplifying means greater than the amplitude of said motion-related signal.

5. The intrusion detection apparatus of claim 4 wherein said predetermined range of Doppler frequencies is related to the Doppler frequencies created by selected motion of a target and said motion detection means responds to a predetermined minimum amplitude of said motion related signal of said Doppler frequencies.

6. The intrusion detection apparatus of claim 4 having means to modulate the transmitting means to establish a modulation frequency greater than the frequencies within said range of Doppler frequencies and generating frequency modulation signals in said receiving amplifying means, and said antijam detection means being responsive to signals of a predetermined minimum amplitude greater than the motion related signals and modulation signals.

7. The intrusion detection apparatus of claim 4 wherein said motion detection means includes a triggered switch having an input means connected to the output of the receiving and amplifying means, a first transistor means connected to the switch, said antijam means including a resistor-capacitor high pass filter and diode rectifier network connected to the receiving and amplifying means, a second transistor means connected to the network, an alarm means connected in series with both of said transistors, and means biasing said transistor means to conduct and responsive to an incoming related signal of said receiving and amplifying means to cut off the corresponding transistor and thereby actuate the alarm means.

8. The intrusion detection apparatus of claim 7 having means to modulate the transmitting means to establish a modulation frequency, a supervisory means connected to the receiving and amplifying means and responsive to modulating related signals of a selected amplitude below the amplitude operative to cut off said second transistor means.

9. The intrusion detection apparatus of claim 4 having means to modulate the transmitting means to establish a modulation frequency, a supervisory means connected to the receiving and amplifying means and responsive to modulating related signals of a selected amplitude below said selected minimum amplitude to which said antijam detection means responds, and said modulating frequency being spaced from said motion related Doppler frequencies, a common alarm connected to the output of the motion detection means and the antijam detection means, said antijam detection means, said antijam detection means including an output means and a high pass filter connected to said receiving and amplifying means and to the output means whereby the sensitivity of the antijam detection means increases as the response of the motion detection means decreases.

=9 l i k UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 618 O83 Dated November 2, 1.971

Inventor(s) BILLY BURLEY El" AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, Line 2, cancel "treater" and substitute CLAIM l greater Column 6, Line 35, before "amplifying" insert CLAIM 6 and Column 6, Line 66, after the comma delete CLAIM 9 "said antijam detection means,"

Sigma (3 1nd (1': ale 6 chi r; 16 iih la r of y 97 (SEAL) Abtest:

EDWARD ILFLL'JICHEII ,Jlf. ROBERT GOT'PSCIIALK A blasting Officer Commissioner of Patents USCOMM-DC 60376-P69 ORM PO-1OSD (10-69] a us GOVERNMENT PRINTING orncs: Ins 0-366-334 

1. An intrusion detection system, comprising a microwave transmitter means for radiating a microwave field, a receiving and amplifying means located within said field for receiving said field, motion detection means connected to the receiving amplifying means to detect motion related signals above a first selected amplitude, and an antijam detection means connected to said receiving and amplifying means and responsive to an output signal above a second selected amplitude treater than said first selected amplitude and related to a selected signal driving said receiving and amplifying means into saturation.
 2. The intrusion detection system of claim 1, having an alarm means, and wherein said motion detection means and said antijam detection means are connected to conjointly hold said alarm means in a standby condition.
 3. The intrusion detection apparatus of claim 1 wherein said antijam detection means includes an output means and a high pass filter means connected to the output of the receiving and amplifying means and to the output means whereby the antijam detection means response increases as said motion detection means response decreases.
 4. In an intrusion detection apparatus having a microwave transmitting means and a receiving and amplifying means, motion detection alarm means responsive to a motion-related signal within a predetermined range of Doppler frequencies and of selected normal maximum amplitude, and an antijam detection means connected to said receiving and amplifying means and constructed to respond to a selected minimum amplitude output of the receiving and amplifying means greater than the amplitude of said motion-related signal.
 5. The intrusion Detection apparatus of claim 4 wherein said predetermined range of Doppler frequencies is related to the Doppler frequencies created by selected motion of a target and said motion detection means responds to a predetermined minimum amplitude of said motion related signal of said Doppler frequencies.
 6. The intrusion detection apparatus of claim 4 having means to modulate the transmitting means to establish a modulation frequency greater than the frequencies within said range of Doppler frequencies and generating frequency modulation signals in said receiving amplifying means, and said antijam detection means being responsive to signals of a predetermined minimum amplitude greater than the motion related signals and modulation signals.
 7. The intrusion detection apparatus of claim 4 wherein said motion detection means includes a triggered switch having an input means connected to the output of the receiving and amplifying means, a first transistor means connected to the switch, said antijam means including a resistor-capacitor high pass filter and diode rectifier network connected to the receiving and amplifying means, a second transistor means connected to the network, an alarm means connected in series with both of said transistors, and means biasing said transistor means to conduct and responsive to an incoming related signal of said receiving and amplifying means to cut off the corresponding transistor and thereby actuate the alarm means.
 8. The intrusion detection apparatus of claim 7 having means to modulate the transmitting means to establish a modulation frequency, a supervisory means connected to the receiving and amplifying means and responsive to modulating related signals of a selected amplitude below the amplitude operative to cut off said second transistor means.
 9. The intrusion detection apparatus of claim 4 having means to modulate the transmitting means to establish a modulation frequency, a supervisory means connected to the receiving and amplifying means and responsive to modulating related signals of a selected amplitude below said selected minimum amplitude to which said antijam detection means responds, and said modulating frequency being spaced from said motion related Doppler frequencies, a common alarm connected to the output of the motion detection means and the antijam detection means, said antijam detection means, said antijam detection means including an output means and a high pass filter connected to said receiving and amplifying means and to the output means whereby the sensitivity of the antijam detection means increases as the response of the motion detection means decreases. 